This invention relates to a new and improved method for producing articles from thermoplastic preforms or parisons, and more particularly relates to picking up and carrying parisons from a pickup station to mold means and then transferring the molded articles from the mold means to a discharge station.
In various known molding techniques, such as vacuum molding, blow molding, or the like, a preform of moldable thermoplastic material, commonly referred to as a parison, is reshaped into a finished article on or within a mold. For blow molding, tubular parisons are provided, and by way of example, the present invention will be described as useful in connection with blow molding, although not intended to be limited thereto.
Although the parisons may be formed by extrusion in a hot state and while still hot be carried to the mold, a widely used procedure comprises cooling the extruded parisons and storing the same for use at a subsequent time. The latter procedure is referred to as a "cold parison" process because it starts with a cold, i.e., room temperature, parison which must be heated to a temperature suitable for molding. Regardless of which procedure is employed, a problem arises in transferring the heated parisons to the mold or molds. By way of example, U.S. Pat. No. 3,566,441 is referred to for an arrangement wherein injection molded parisons are transferred directly from the injection mold to a blow mold. An example of apparatus for transferring reheated or oven heated parisons to blow molds is found in U.S. Pat. No. 4,106,886. Although the first mentioned patent discloses a rotating arm device, and the second mentioned patent discloses a linear transfer device, neither of such patents discloses any molded article stripping and/or transfer means for clearing the mold or molds of molded articles. In other words, the disclosed apparatus of the identified patents are designed for the single purpose of transferring parisons from a parison forming mold to a blow mold and then a repeat of that operation. Some other not disclosed means, in no way directly associated with the parison transfer and blow mold loading means must be employed.
Even though the art of molding articles from thermoplastic parisons has, as represented by the foregoing patents, attained a considerable state of development, there nevertheless remains the desirability of increasing the production rate without increased cost, utilizing the heating oven to greater advantage by more rapid transfer of heated parisons to the molds. It is also desirable to attain more rapid transfer from oven to blow molds and transfer of articles from the blow molds, rapidly and with minimum dwell intervals.